Semi-rigid polymer encapsulated filter medium containing an unencapsulated adsorbent material



April 2, 1968 c. A. RODMAN 3,375,933

SEMI-RIGID POLYMER ENC-APSULATED FILTER MEDIUM CONTAINING ANUNENCAPSULATED ADSORBENT MATERIAL Filed Feb. 1, 1965 2 Sheets-Sheet 1F'IGJ.

SINTERED BLEND OF POLYMER ENCAPSULATED SOLID AND ADSORBENT SUBSTANCE Aril 2, 1968 c. A. RODMAN 3,375,933

SEMI-RIGID POLYMER ENCAPSULATED FILTER MEDIUM CONTAINING ANUNENCAPSULATED ADSORBENT MATERIAL l I l I l l l o o o o o o o O o 9 00 hw m r m m VAOWEH 3A0 .40 AQNEIDHAB QQVd HIONIS United States PatentOfiice 3,375,933 Patented Apr. 2, 1968 3,375,933 SEMI-RIGID POLYMER ENCAPSULATED FILTER MEDIUM CONTAINING AN UNENCAPSULATED ADSORBENT MATERIALClarke A. Rodrnan, Riverside, R.I., assignor to Fram Corporation,Providence, R.I., a corporation of Rhode Island Filed Feb. 1, 1965, Ser.No. 429,215 1 Claim. (-01. 210-502) ABSTRACT OF THE DISCLOSUREAdsorption filter for removing dissolved impurities from fluid.Unencapsulated absorbent particles (e.g., activated carbon) aresupported in a semi-rigid matrix formed of a sintered mass of solidsencased in thermoplastic polymer casings, said encased solids beingattached to each other by thermoplastic bonds between the casings toform the semi-rigid matrix.

The present invention relates to filter media and partricularly to fixedbed media for filtering fluids. The filter media of the invention areformed of intimate heterogeneous mixtures which media are sufficientlrigid to retain their original shape and yet avoid compaction duringuse.

More specifically, the invention resides in filter H1Cll21l:0f liquidsand gases which media are comprised of a $111- tered mixture of afree-flowing powder of polymer encased or encapsulated individualdiscrete particles of a finely-divided solid with a finely-dividedabsorbent, ion exchanger, or filter aid. The filter media of theinvention have excellent filtering properties, a long filtering life,permit rapid flow of fluid through the media with a low pressure dropacross the filter media.

The rapid-flow property of the filter media is particularly importantsince it is not only possessed by the media when freshly formed, but itis retained over long periods of usage in filtration operations. Thisretention of the free-flow property is a unique characteristic of thefilter media of the invention. It is made possible by virtue of the factthat these filter media resist compaction of the mass during usage. Thisresistance to compaction of the filter media results from the semi-rigidstructure of the matrix formed upon sintering the mixture of polymerencased or encapsulated solids and the finely-divided adsorbentsubstance. The matrix consists of the polymer encased solid. It isdesirable to employ polymer encapsulate material which is non-volatileand which will not affect the adsorption or chemical proprties of theadsorbent, ion exchanger, or filter aid.

Another important property of the filter media of the invention is theelficient and effective filtration of fluids which it provides at highrates of the fluid flow and the effective removal of impurities madepossible per unit of weight of adsobent, ion exchanger, or filter aidpresent in the media. The filter media of the invention provide for theremoval of greater amounts of dissolved impurities from a fluid per unitof adsorbent substance, such as activated carbon.

It has been proposed heretofore and in presently marketed filter mediato pack a container or cartridge with loose powder or granules ofadsorbent, ion exchanger, or filter aid, such as activated carbon. Insuch a filter, the fluid, such as a liquid, is permitted to flow orpercolate through the mass of adsorbent, ion exchanger, or filter aid.This packing of loose filter aid may permit rapid flow of the fluid atfirst, but after very little usage in filtration the particles of filteraid tend to settle and pack in the cartridge, thereby forming a morecompact mass. Under these conditions of compaction the pressure dropacross the filter is greatly increased and there is also danger ofchanneling of liquid passing through the filter which would drasticallyreduce the filters efliciency. Consequently, the useful life of thefilter is greatly reduced. One of the contributing causes of theshortened life of these prior art filters is that as a result of thecompaction of the mass, a substantial portion of the filter aid is nolonger made accessive to the fluid flowing through the mass. Thisresults from the channeling of the fluid in the mass and the reducedapparent surface of filter aid exposed to the fluid soon becomesexhausted.

Efforts have been made to overcome these difliculties encountered in theloosely packed filters and to prevent compaction of the filter aidduring use. One result of such efforts has been to employ largergranules of the adsorbent, ion exchanger, or filter aid instead of thefinely-divided forms. These loosely packed large granules of adsorbent,ion exchanger, or filter aid are less prone to compact during use thanthe finely-divided forms, but they possess other serious disadvantages.Being much larger particles they possess much less apparent surfacearea, thereby drastically reducing the instantaneous adsorbent capacityper unit of weight of the filter aid or adsorbent substance. Since theypossess much lower instantaneous efficiencies for removing impuritiesfrom fluids, it therefore becomes necessary to pass the fluid through alonger bed of filter aid to provide satisfactory purification of thefluid.

It is therefore an object of the present invention to overcome theshortcomings of prior art adsorption filter media.

It is another object of the invention to provide filter media whichpermit rapid flow of fluids through them over longer periods of usage infiltration operations, which media resist compaction during usage, andwhich provide highly efiicient removal of dissolved impurities fromfluids per unit of weight of adsorbent, ion exchanger, or filter aid.

It is a further object of the present invention to provide filter mediafor fluids which media are comprised of a sintered mixture of afree-flowing powder of polymer encased or encapsulated individualparticles of a finely-divided solid with a finely-divided adsorbent, ionexchanger, o-r filter aid.

The novel filter medium of the invention thus comprises a sintered massof solids encased in thermoplastic polymer casings, the encased solidsbeing attached to each other by portions of their casings to form asemi-rigid matrix, with finely divided particles of adsorbent materialdistributed throughout the mass and mechanically sup ported by thematrix between the polymer encased solids, the particles of adsorbentmaterial being unencapsulated.

Other objects of the invention will be apparent to those skilled in thefilter art from reading the present specification, taken in conjunctionwith the accompanying drawings, in which:

FIG. 1 is a top plan view with portions cut away of a substantiallyrigid filter medium produced in accordance with the present invention,showing the sintered blend of adsorbent substance and polymerencapsulated solid.

FIG. 2 is a perspective side view of the filter medium of FIG. 1, withportions cut away.

FIG. 3 is a vertical partial sectional view through a filter employingthe filter medium of FIGS. 1 and 2 and Example 1, showing portions ofthe contents of the filter medium.

FIG. 4 is a graph comprising the life characteristics and filteringefiiciency of a filter employing the medium of Example 1 with twopresently available commercial filters.

The benefits of the present invention are achieved by means of asintered unitary mass comprising a matrix of polymer encapsulated orencased solid holding between the solids unencapsu-lated particles of afinely divided adsorbent, ion exchanger, or filter aid. The adsorbent,ion exchanger, or filter aid is a substance which is normallyfree-flowing and which if employed alone in a filter unit would compactand tend to restrict the flow of fluid through the mass. The polymerencapsulated solid is one which prior to sintering is normally alsofree-flowing and which per se does not impart any adsorbtion property tothe filter mass. When sintered, the thermoplastic polymer encapsulatedparticles sinter together sufliciently to form a semi-rigid framework ormatrix about the particles of adsorbent, ion exchanger, or filter aid.The sintered mass is compacted insufiiciently to inhibit seriously theflow of fluid through the mass.

The filter media of the invention can be produced by first blendingfree-flowing thermoplastic polymer encapsulated solid particles and afinely-divided adsorbent, ion exchanger, or filter aid in the desiredproportions. The blend is then placed in or extruded into a chamber,

form or mold of a shape which it is desired to have the filter mediaassume. The mass is then subjected to sufiicient heat to cause thethermoplastic polymer casings to sinter slightly and to become attachedto one another thereby forming the highly important matrix which locksthe particles of adsorbent, ion exchanger, or filter aid into place andprovides the unitary filter medium. The filter medium will assume theshape of the chamber, form or mold in which the mass is placed prior tothe sintering operation. The shape of the filter medium is not criticaland may vary according to use to which the filter medium is to besubjected.

The sintering operation is readily accomplished by subjecting the blendof thermoplastic polymer encapsulated solid and adsorbent substance inthe form to the action of heat. Temperatures of 300 F. and above areusually sufficient, with the desired temperature depending somewhat uponthe nature of and the molecular weight of the thermoplastic polymerencapsulation. The higher molecular weight polyolefins, for example,will permit the use of "higher temperatures. With polyethyleneencapsulated solids the temperature of 300 F. is usually suitable. It isdesirable to employ a non-oxygenous atmosphere, such as nitrogen, orhydrogen, or high pressure steam so as to prevent combustion of thepolyolefin during sintering. It has been found desirable to add anantioxidant to the blended mass prior to sintering so as to prevent thepossibility of combustion during sintering. One suitable antioxidant isSantonox (containing as the active ingredient,4,4bis[3-methyl-6-tertiary butyl phenol1), in an amount of about 0.5% byweight of the polyolefin encapsulated component. Satisfactory resultshave been obtained with the antioxidant treated polyolefin encapsulatedcomponent in hot air up to 450 F. without combustion. It has also beenfound that the use of a perforated mold to flow heated air, inert gas,or high pressure steam through the bed accelerates the bonding orsintering rate.

The sintering operation can provide various degrees of compaction of thefilter medium. The higher the temperature, the longer the duration ofthe sintering time and the greater the pressure applied to the mass, thegreater will be the compaction of the mass, including the sinteredmatrix of polymeric encapsulated particles. The greater the compactionof the mass during sintering, the lower will be the permeability of thefilter medium and the lower the rate of flow of fluid through the filterduring filtration. For some types of filtration a more compact filtermedium is desirable, but since most filtering operations require maximumflow rate, it is usually preferred to sinter and compact the mass aslittle as possible. In such cases it is desirable to sinter the masssufficiently to form only a matrix of polymer encaspulated particleswhich will hold the medium together and prevent settling and motility ofthe particles of finely-divided adsorbent, ion exchanger, or filter aidduring filtering operations.

It is also possible to extrude and sinter in place a rigid porous fixedbed shape or article by preheating the blend of encapsulated materialand adsorbent, ion exchanger, or filter aid by means of a hot gasfluidized bed within at most 5 F. below the stick point of the polymerencapsulate, screw feeding the preheated mixture into a heated mold dieheld at a temperature sufficient to sinter the polymer encapsulate andthen through a cold mold die to set the bonded structure.

As will be apparent from the foregoing, where maximum rate of flow offiuid is desired through the filter, the sintering treatment should beno more than moderate. Excessive temperature, time or pressure will allcontribute to excessive compaction and if the conditions of sinteringare severe enough, the mass will sinter and compact to a degree that itmay become substantially impervious to the flow of fluids. For most usesit is desirable that filter medium permit a fiow of air of at leastabout 0.2 to 3 cu. ft. per minute when subjected to a pressure head of0.5 inch of water.

The nature of the polymer encapsulating the solid particles of theencapsulate component may vary depending upon the nature of the fluid tobe filtered. The selection of the polymer to be employed should begoverned by the requirement that the polymer must not be subject toundue decomposition during the thermal sintering operation in which thefilter is formed. The polymer should be thermoplastic so as to sinter atreasonable temperatures, should be non-volatile in nature and should notaffect the adsorption or chemical properties of the adsorbent, ionexchanger, or filter aid. It should not be dissolved or decomposed bythe fluid which is to be filtered. Among the polymers which may beemployed are the polyamides, such as nylon; the polyesters, such asterylene; the vinyls, such as polyvinyl chloride; the acrylics, such aspolymethylmethacrylate. For most uses the polyolefins, such aspolyethylene and polypropylene, have been found to be most useful andare preferred for most applications.

The preferred polyolefin encapsulated solid component of filter media ofthe invention is desirably of the type sold by National Lead Companyunder the trademark Nalcon. These materials are normally free-flowingpowders of individual particles, each particle being encased orencapsulated in a shell of a polymer of an aliphatic l-olefin monomercontaining less than 6 carbon atoms, such as ethylene, propylene,butene-l, and the like. The encased solid particles may be of almost anynature provided that it is possible to encase them in polyolefin.Desirably the encased particles are short fibers, such as cellulosefibers, including kraft fibers, cotton fibers and linters, shreddedwood, wood pulp fibers and the like, wool fibers, steel or metal woolfibers, glass or asbestos fibers, etc. Also the encased particles may benon-fibrous particles, such as metal powder particles, includingaluminum and copper powder particles, nonmetallic particles, such ascarbon particles, particles of silicates, such as sodium or calciumsilicates, etc., titanium dioxide, and the like.

While the polymer encapsulated particles may be fibrous or non-fibrous,it is preferred that the particles be fibrous in nature since they seemto provide superior results. Fibrous materials may be characterized ashaving a length at least about 5 times the thickness, with a preferredlength of at least to microns up to about 0.5 inch or more.

Among the preferred polyolefin encapsulated materials which may beemployed are those described in Orsino et al. US. Patent No. 3,121,698,granted Feb. 18, 1964, Orsino et al. Canadian Patent No. 678,341,granted Jan. 21, 1964-, and Belgian Patents Nos. 575,559; 578,868;580,554; 594,911; 601,734 and 601,325. It is intended to incorporate byreference the disclosures of these patents in their entireties.

The adsorbent, ion exchanger, or filter aid component of the filtermedia are finely-divided materials which are well known in thefiltration art. These substances are capable of removing dissolvedand/or colloidally dis persed substances from a fluid by severalphenomena, including chemical attraction or reaction, physicalattraction or mass action. Included among these well-known materials areion exchange resins, such as sulfonated or carboxylated styrene anddivinyl benzene copolymers, quaternary ammonium alkyl substitutedstyrene and divinyl benzene copolymers, powdered zeolite (both naturaland synthetic) and the like, diatomaceous earth, activated carbon,activated alumina, activated silica gel, Fullers earth, montmorillonite,bentonite and surface active clays in general, the molecular sieves etc.Mixtures of these substances may be employed. The substance selectedwill, of course, depend upon the nature of the impurity to be removedfrom the fluid.

In Table I below are listed some of the adsorbent, ion exchanger, orfilter aids which may be selected for removal of various dissolvedimpurities from various fluids.

TABLE I Fluid to be purified Function of Filter Aid Adsorbcnt, IonExchanger, or Filter Aid Water Purification and remov- Activated carbon.

91 of dissolved gases and taste producing substances.

Water Removal of dissolved Ion exchange resin.

minerals.

Dry cleaning fluid Decolorization and re Activated carbon.

moval of odors, grease and soaps.

Hydrocarbon fuels and Removal of suriacants Do.

organic solvents. and dissolved organic contaminants.

Water or organic Removal of colloidal Dlatomaceous earths,

solvents. contaminants in col- Fullers earth or loid suspension.activated alumina. Air or gases Removal of unwanted Activated carbon,

gases in solution or molecular sieves, suspended liquids. silica gel.Organic solvents or Removal of dissolved Silica gel, activated gases.water. alumina or molecular sieves.

It is also contemplated that a mixture of filter aids, ion exchangers oradsorbents may be employed in the same filter medium. Thus, for example,it is frequently desirable to employ both activated carbon and an ionexchange resin in the same filter medium.

The particles of filter aid, adsorbent, or ion exchanger component mayvary over a wide range of average particle sizes. Of course, the largerthe particle size, the lower is the apparent surface area per unit ofWeight of the substance. As has been explained hereinabove, one of thediificulties with prior art filter media is the need to employ adsorbentsubstance in the form of large granules if compaction and restriction offluid flow is to be counteracted. One of the important advantages of thepresent invention is that the adsorbent substance can be infinely-divided form and, therefore, of small particle size.Consequently, a large apparent surface area of adsorbent is exposed forfiltration purposes. This means that a more effective and efficient usemay be made for each unit of weight of adsorbent substance. Thusparticles having an average particle size of less than 100 mesh (US.Standard Sieve Series) may be employed. In fact, it is usually preferredto employ particles small enough to pass through a 300 mesh screen, orsmaller. The use of pulverized powders has been found to be particularlyeffective and efiicient.

The proportions of polymer encapsulated solid and the adsorbent, ionexchanger, or filter aid employed may vary widely. It has been founddesirable for optimum efficiency in my novel filter media to employ aslittle as possible of the polymer encapsulated moiety, since it performslittle or no role in removing impurities dissolved in the fluid beingfiltered. The role of the polymer encapsulated moiety is to provide,after sintering, a framework or matrix which holds the adsorbentsubstance in place and yet prevents compaction of the filter mediumduring usage. It is preferred to employ at least about 25% by weight ofthe polymer encapsulated substance, based on total weight of the medium,in order to insure sufiicient bonding of the mass upon sintering. Whenamounts in excess of 90% by weight of polymer encapsulated solid areemployed, the efiiciency of the filter medium isreduced, since thismatrix component contributes little to the removal of dissolved solids.

The preferred proportions of polymer encapsulated component in thefilter medium will depend to some extent upon the amount of polymerencapsulated about the individual solid particles. With larger amountsof polymer encapsulation, it is normally possible to employ smallerproportions of the encapsulated solid. However, it is desirable toemploy encapsulated particles consisting of not in excess of 75% byweight of polymer, since larger amounts tend to produce shrinkage anddistortion of the media during the sintering treatment. For best resultsit is preferred to employ an encapsulated moiety containing at leastabout 50% by weight of polymer.

The use of polymer encapsulated solids in filter media of the inventionis important. In addition to providing the matrix which preventscompaction during use, it provides for mechanical filtration and removalof suspended solids from the fluid. If particles of polymer above(without encapsulation in a solid) are employed, the rigidity andfreedom from compaction would not :be obtained. The presence of theencapsulated solid particles is necessary to survive the sinteringtreatment. Even after sintering the polymer remains encapsulated aboutthe solid particle without coating the adsorbent, ion exchanger, orfilter aid. To provide this property it is particularly desirable toemploy encapsulated solids in which the solid is in the form of a fiber.The polyolefin encapsulation is particularly preferred because of itsunique inertness to most fiuids to be filtered.

Filter media of the invention may be formed in various shapes and sizesdepending upon the volume and nature of fluid to be filtered. Onesuitable shape is that illustrated by the drawings, but otherconfigurations may be employed with satisfactory results.

In order more clearly to disclose the nature of the pres- .entinvention, the following examples illustrating the invention areprovided. It should be understood, however, that this is done solely byway of example and is intended neither to delineate the scope of theinvention nor limit the ambit of the appended claims. Unless otherwisestated, parts and percentages are intended to refer to parts by weightor percent by Weight.

Example 1 The filter medium of this example will be described inconjunction with the accompanying drawings.

A mixture was prepared of 408 grams of activated carbon of an averageparticle size of less than 1000 mesh and 204 grams of Nalcon (comprisingindividual fibers of Solka Floc, ground purified paper pulp,encapsulated with polyethylene in an amount of 75 by weight of theencapsulated product, produced in accordance with Orsino et a1. PatentNo. 3,121,698) and which had been treated with one gram of Santonoxantioxidant. Enough of the resulting blend was then placed in a moldhaving a cavity registering with the shape of the filter unit shown inFIGS. 1, 2 or 3 to fill the mold. Usually, this mold will only take 5grams of blend to fill it. The mold and its contents were placed in amechanical convection oven and the mold was heated at 400 to 450 F. forabout 1.5 hours. The mold was cooled to room temperature, opened and thefilter medium removed. The medium had the form shown in FIGS. 1, 2 or 3of the drawings, in which numeral 10 designates in its entirety themolded depth type of filter medium. The medium is of cylindrical shapeand has a central bore 11. As shown in FIGS. 2 and 3 it may be providedwith a perforated center tube, such as indicated by 12 and 16,respectively.

A preferred embodiment of a fluid filter employing the filter medium ofthe invention is illustrated by FIG. 3.

In this unit the substantially rigid filter medium is placed in thefilter housing 15, with the medium fitting over the perforated centertube 16, and having interposed between the medium 10 and the center tube16 an inner wrap 17 consisting of a sheet of micro glass fibers andDacron (polyester) paper having a filtration rating of less than 1micron. Interposed between the housing and the medium 10 is an outerwrap 18 consisting of a sheet of Vinyon, Dacron and fine glassfibers. The entire unit is contained within the shell 30. The unit isequipped with inlet and outlet 21.

The filter medium of the foregoing example employed in the filterdescribed hereinabove in conjunction with FIG. 3 was then tested tocompare its filtering properties with two currently available commercialfilters of the prior art. Both of these commercial filters employed thetypical packings of loose coarse granular activated particles in apercolation treatment. In Table II below are listed the dimensions ofthe filter media.

5 An experimental filter medium comprising a plug 1% diameter 1 inchlong was fabricated out of an intimate blend of 9 grams of micropowdered mixed bed ion exchange resin comprising 59% by wt. Rohm & HaasAmber-lite XE-59 an anion exchange resin in the free base 10 form ofparticle size smaller than 325 mesh and 41% by wt. Rohm & Haas AmberliteXE-97 a cation exchange resin in the hydrogen form of particle sizesmaller than 325 mesh and 3 grams of polyethylene encapsulated paperpulp of the same composition as described in Example 1.

15 The polyethylene encapsulated paper pulp and rest of the mix wereheat molded at 300 F. for 45 minutes in a glass funnel test fixturepreviously coated with a Hycar adhesive. A special test water comprising0.2265 gram calcium chloride (CaCl 0.183 grams magnesium chloride TABLEII Example 1 Commercial A Commercial B Filter bed dimensions 3.5 inoutside diameter, 1.2 in. 3.0 in. outside diameter, 1.0 in. 3.0 in.outside diameter, 1.5 in. inside diameter, 12 in. long. inside diameter,7 in. long. inside diameter, 3.5 in. long. Flow pattern-.- Radial End toend Radial. Depth of pass 1.19 inches 7 inches 0.56 inches. Grams ofactivated carbon 390, less than 325 mesh 258, 12-30 mesh 93, 8-12 mesh.

and mesh size.

Test water containing methylene :blue was passed through each of thethree filters to test the ability of the filters to remove the dye fromthe water and the drop in liquid flow rate observed during the test. Thetreatment of each filter was identical. The test employed was anadaptation of the method described in Active Carbon by Hassler, pp.340-343, Chemical Publishing Co., Inc., New York (1951). In the courseof the test fresh methylone blue was added to the test water at the rateof 5 cc. per minute of a solution containing 2.5 gms. of methylene blueper liter.

A comparison of the test results is shown in Table III below:

(MgCl -6H O) and 3000 grams of demineralized water was reservoir fed tothe test fixture under various air pressure heads varying from 1-5inches of mercury. The number of seconds required to obtain two sets of50 ml. of water each flowing from the test fixture were recorded. Thefirst 50 ml. of each sample set was analyzed for hardness by theethylene diarnine tetraacetic acid (EDTA) method described in StandardMethod for the Examination of Water & Waste Water, American PublicHealth Association, N. Y., 11th Ed. 1960, page 133. The second 50 ml.effiuent sample was analyzed for chloride ion in accordance with themercuric nitrate method described in the same source as the hardnessmethod, page 79. The

TABLE III Example 1 Commercial A Commercial B Gallons of Water Filtered2, 400 1, 500 200.

to Elution-Carbon Capacity Rated Flow 1 gallon per minute 0.5 gallon perminute 0 5 gallon per minute,

Single Pass Initial Eficient 99%, remains constant for first 2,000gallons passed.

99%, drops off within first 100 gals. passed.

%, drops ofi immediately.

The actual test results are plotted on the graph shown inFIG. 4.

As shown by the foregoing test results, the filter medium of theinvention provides for much more rapid fiow of liquid through the filterand what is particularly desirable is the retention of the high flowrate over vastly longer periods of operation than is permitted by thetwo commercially available filters. Also of great significance inpractical operation is highly eifective purification obhardness iscalculated in ppm. of hardness as calcium 50 carbonate (CaCO which is anindication of the presence of both the calcium and magnesium cations inthe test water. The chloride determination is an indication of thepresence of chloride anions in the test water. The presence of nohardness and chloride components in the etfiuent water indicatescomplete demineralization by the filter medium. The results of this testare given in Table IV below:

TABLE IV Air Pres- Accumu- Seconds to Hardness, Hardness Chloride,Chloride sure Head, lative Test obtain 50 parts per Removal parts perRemoval inches Etlluent ml. of water million, efi., million eti, mercuryml. Efiluent CaCO; Percent Percent parts per million.

Nora-The test water had a hardness of 130 parts per million and achloride content of 70 parts per million.

Example 3 Experimental filter media comprising plugs 1% diameter 1 inchlong were fabricated out of an intimate blend of 75 parts offinely-divided activated carbon (Darco G- 60) of particle size smallerthan 325 mesh and 25 parts of polyethylene encapsulated paper pulp ofthe same composition as described in Example 1. One portion of themixture of polyethylene encapsulated paper pulp and activated carbon wasmold-ed at 300 F. for 45 minutes in a glass funnel test fixturepreviously coated with a Hycar adhesive. The other portion was looselypacked (without being subjected to the heat treatment) in the form of aplug the same size. Water was reservoir fed to the test fixture underair pressure heads of one and five inches of mercury. The number ofseconds required to obtain two sets of 50 ml. of water each flowing fromthe test fixture were recorded at the beginning and after being usedovernight. The results were as follows:

Pressure Time Required in Seconds As shown by the foregoing results, thesintered filter medium of the present invention permits more rapid flowthan a filter medium of the same composition, but not sintered, and thesintered filter does not tend to compact during usage as shown by thefact that the flow rate is about the same after standing overnight.

As used herein, and in the appended claims, the term adsorbent substanceis intended to refer and encompass adsorbents, ion exchangers, andfilter aids, these being materials known for their ability to removedissolved materials from fluids and which materials are substantiallyinsoluble in the fluid being treated. The term adsorbent is a wellrecognized term, known even to the layman, and

is used herein in its usual broad sense to connote a substance whichtakes up and holds another substance by adsorption, in accordance withWebsters Third International Dictionary. The same source of Websterdefines adsorption as a taking up by physical or chemical forces ofmolecules of gas, dissolved substances, or of liquids by the surfaces ofsolids with which they are in contact. This is what is contemplated andencompassed by the present invention.

The terms and expressions which have been employed are used as terms ofdescription and not of limitation, and there is no intention in the useof such terms and expressions of excluding any equivalents of thefeatures shown and described or portions thereof, but it is recognizedthat various modifications are possible within the scope of theinvention claimed.

What is claimed is:

1. A filter medium comprising (A) a sintered mass of solids encased inthermoplastic polymer casings said encased solids being attached to eachother by portions of their casings to form a semi-rigid matrix, and

(B) finely divided particles of adsorbent material distributedthroughout the mass and mechanically supported by the matrix betweensaid polymer encased solids, said particles of adsorbent material beingunencapsulated.

References Cited UNITED STATES PATENTS 3,019,127 1/1962 Czerwonka et al.

3,121,698 2/1964 Orsino et al. 260-2.5 3,165,470 1/1965 Giesse et al55-524 X 3,212,641 10/1965 Komarmy et al. 210-504 X MURRAY KATZ, PrimaryExaminer. LEON D. ROSDOL, Examiner. I. GLUCK, Assistant Examiner.

